JP2000340916A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board, where the existence and stress distortion on not only the surface layer part of the board but also on an inner layer part are measured and various influences by means of distortion can be dissolved at measuring the state change of a distortion gauge due to distortion by stresses in the printed wiring board. SOLUTION: In a printed wiring board 1 formed of a board 3, where plural insulating boards 2 are stacked and a conductor pattern formed on the surface layer of the board 3, metal foil 10 whose conductor resistance change is large is buried in the inner layer of the board 3. Measuring electrodes 15 for connecting them to metal foil 10 are arranged on the surface of the board 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring stress distortion in an inner layer of a printed circuit board by measuring a change in state such as distortion caused by stress in the printed circuit board by replacing the change in conductor resistance of a metal body provided in the inner layer of the printed circuit board. The present invention relates to a printed wiring board capable of measuring the presence and the value of, and eliminating various effects due to distortion.

[0002]

2. Description of the Related Art At present, various failures have occurred in electrical parts (electrical parts), mechanical parts, and the like constituting various precision instruments and mechanical devices due to causes that are difficult to visually confirm. . Such causes include, for example, temperature, magnetism, static electricity, stress distortion, and the like. Changes and adverse effects caused by the causes of various failures cannot be simply measured, and a large-scale device is often required to measure them. For example,
Regarding the measurement of strain due to stress, measurement using a strain gauge is generally performed, and in a mechanical device or the like, strain measurement using the strain gauge is performed in many situations.
As is well known, a strain gauge is a means for converting a physical quantity such as pressure, load, displacement, or the like into an electric signal. For example, a piezoresistive effect that an electric resistance value changes when a strain is applied to a resistor such as a metal or a semiconductor. This is a stress measuring means utilizing the above.

[0003] By the way, the printed wiring board as an electric component used for the electrical component of various devices has conventionally been subjected to distortion measurement when it is mounted on the device by a method such as screwing. Was almost never measured. However, with regard to recent printed wiring boards, a large number of components are often mounted due to high-density mounting.
A lot of micro chip parts for which solder connection reliability is a concern, and BGAs and CSPs for solder ball connection, etc. have been increasingly included. Each of these mounted components is a component that may be deteriorated in solder connectivity with a substrate due to slight distortion of the printed wiring board itself. In addition, if the board is bent or deformed by warping due to the stress due to the weight of the mounted parts, the thermal stress applied during reflow connection or flow connection, or the thinning of the printed wiring board, the mounted chip components such as chip resistors Various obstacles such as chip cracks in which cracks are formed occur, and the effects caused by the distortion of the printed wiring board cannot be ignored. For this reason, by measuring and knowing in advance the distortion applied to the required portion of the printed wiring board and the resulting effect, measures have been taken to avoid problems such as poor connection of parts and deterioration in support stability. Therefore, it is necessary to reduce the incidence of defective products. In other words, by acquiring data on the distortion that occurs when the printed wiring board is mounted on the actual machine, it is possible to change the arrangement of components and select a board thickness that is not easily deformed at the design stage. Becomes By the way, as a means for measuring the strain applied to the printed wiring board or the like, for example, it is conceivable to measure the strain by attaching a strain gauge to an appropriate place of the printed wiring board. The problem of securing the space for attaching the gauge, the problem that it is difficult to measure the strain in the state of being assembled to the device because the printed wiring board with the strain gauge attached cannot be assembled to the device, the measurement only on the surface layer of the wiring board Therefore, there is a problem that the measurable portion is limited to a local area and becomes insufficient, and a problem that the cost of the strain gauge itself increases.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has been made in consideration of a state in which a state change such as a strain due to a stress generated in a printed wiring board is measured by a strain gauge.
It is an object of the present invention to provide a printed wiring board capable of measuring the presence and value of stress strain not only in a surface layer portion of a substrate but also in an inner layer portion and eliminating various effects due to the strain. That is, the strain gauge used for the strain measurement of the present invention is formed of a thin metal foil made of a material having a piezoresistive effect, and a small resistance change generated in the metal foil due to stress or the like is distorted. The amount of distortion is measured by converting it into a quantity, but the printed wiring board originally has copper foil on the inner layer, and the inner layer also has a metal foil with a large change in conductor resistance.
For example, it is considered that a metal box made of Ni or the like is provided in one inner layer, and a strain gauge is formed by photoetching, so that it can have a role of a simple strain gauge.

[0005]

In order to solve the above-mentioned problems,
According to a first aspect of the present invention, in a printed wiring board comprising a substrate on which a plurality of insulating plates are stacked and a conductor pattern formed on at least a surface layer of the substrate, a metal foil having a large change in conductor resistance is embedded in an inner layer of the substrate. It is characterized by having done. The invention according to claim 2 is characterized in that a measurement electrode for connecting to the metal foil is arranged on a surface layer of the substrate. The invention according to claim 3 is characterized in that nickel is used as the metal foil having a large conductor resistance change. The invention according to claim 4 is characterized in that the metal foil is formed on an insulating plate by photoetching. The invention of claim 5 is characterized in that a plurality of the metal foils are arranged at arbitrary positions on one insulating plate constituting the substrate. The invention of claim 6 is characterized in that a plurality of the metal foils are arranged on one insulating plate, and the directions of the metal foils are set in multiple directions. The invention according to claim 7 is characterized in that the metal foils are arranged at arbitrary positions on different insulating plates constituting the substrate. The invention according to claim 8 is characterized in that the metal foil and the measurement electrode formed on the surface layer of the substrate are connected by through holes. According to a ninth aspect of the present invention, the through hole is formed by plating a solder in a hole formed in the substrate. The invention according to claim 10 is a printed wiring board comprising a substrate on which a plurality of insulating plates are laminated and a conductor pattern formed on at least a surface layer of the substrate; The present invention is characterized in that the metal foils are arranged on the back surface of the substrate corresponding to the metal foil on the front side, respectively, and both metal foils are connected by through holes.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is an external perspective view of an example of a printed wiring board to which the present invention is applied. A strain gauge is provided on an inner layer of a printed wiring board 1 formed by laminating thin plates (insulating plates) made of an insulating material such as glass epoxy. The number of metal foils (metal foil gauges) 10 to be used as a plurality is arranged at an arbitrary position in an arbitrary layer and in an arbitrary direction. That is, the printed wiring board 1 includes a substrate 3 formed by laminating and integrating a plurality of insulating plates 2, a surface conductor pattern formed on the front surface or the back surface of the substrate 3, and a space between the insulating plates, that is, formed on the inner layer of the substrate. Inner conductor pattern 4 and the like. Ideally, each metal foil 10 is formed by, for example, photoetching into a shape as shown in FIG. Terminal portions 10a, 1 at both ends of the metal foil 10
0b are connected to electrodes exposed on the surface layer (front surface and / or back surface) of the wiring board, respectively, and the electrodes are connected to measurement terminals of a measuring device (not shown), respectively. The strain caused by the stress on the portion can be measured electrically. As a material of the metal foil 10, for example, a metal material such as nickel Ni having a piezoresistance effect is used. As a material of the metal foil 10, even if it is other than Ni, a metal material having a large change in conductor resistance can be used. The reason for disposing the metal foil 10 in the inner layer of the substrate 3 is that the outer surface of the substrate is often used as a component mounting space or other area, so that the metal foil 10 cannot be stuck. Sometimes, the metal foil 10 is formed on the insulating plate 2 by a method such as photoetching, so that the metal foil serving as a strain gauge is continuously incorporated in the completed printed wiring board. It is possible to measure the state of occurrence of distortion at any time. By using the metal foil 10 as a built-in strain gauge, there is no need to prepare a large number of strain gauges as in the prior art, and it is not necessary to secure a space for pasting, and no setup or procedure for pasting or peeling is required. And handling,
Measurement work is facilitated. When a strain gauge is attached only to the outer surface of the substrate, only the distortion of the surface layer can be measured. However, by arranging the metal foil inside, the distortion at an arbitrary position inside can be measured accurately.

FIG. 3 is a cross-sectional view of a principal part of a printed wiring board to which the present invention is applied. A substrate 3 having a multilayer structure in which a plurality of insulating plates 2 made of an insulating material such as glass epoxy is laminated on a front surface or a back surface thereof. It has a normal wiring pattern made of copper, aluminum or the like, and if necessary, the wiring pattern is electrically connected to the internal pattern 4 made of copper foil or the like disposed in an inner layer via a through hole 11a. The through holes 11a, 11b, and 11c are formed by coating the inner wall of the hole that does not penetrate the substrate 3 or the periphery of the opening with solder or the like by plating. In this embodiment, the metal foil 10 used as the strain gauge is the second and third layers from the top.
The two terminal portions 10a and 10b of the metal foil 10 are formed between the insulating plates 2 of the layer, and the two terminal portions 10a and 10b are formed by a through hole 11b formed of a hole formed from the substrate surface and a solder formed on the inner wall of the hole. It is electrically connected (connected) to the measurement electrode 15 arranged on the substrate surface. That is, the metal foil 10 having the structure as shown in FIG. 2 is arranged in the inner layer, and the terminals 10a and 10b are respectively connected to the measurement electrodes 15 on the surface via the through holes 11b. The metal foil 10 is energized in a state where the measuring terminal of the measuring device (not shown) is connected to the measuring electrode 15 to convert a minute resistance change into a strain amount to measure the strain. That is, in this embodiment, the metal foil 10 made of a metal material having a large conductor resistance change is connected to the measuring electrode 15 provided on the surface layer of the substrate, so that the printed wiring board is incorporated into the electrical unit of the device body. It is also possible to measure the value of the strain caused by the stress at any time and the effect thereof. As described above, as a metal material having a large change in conductor resistance, a metal foil such as nickel Ni is preferable. This metal foil 10 is preferably formed as a metal foil gauge by photoetching in the same manner as in the step of forming a conductor pattern on each insulating plate. That is,
Without using special technology with high equipment costs and run-in costs,
It can be easily formed by ordinary printed wiring board manufacturing technology, and does not cause an increase in manufacturing cost.

Although not shown, a plurality of metal foils 10 as strain gauges may be arranged at arbitrary positions in the same layer, and the direction of each strain gauge depends on the strain to be measured. May be made different depending on the situation, and as a result, a plurality of metal foils in the same inner layer may be arranged in multiple directions. As a result, it is possible to measure by replacing the state change at each position of the printed wiring board with the electric resistance change, or by replacing the directional state change with the electric resistance change. Further, a metal foil 10 as a strain gauge
May be arranged between different insulating plates, that is, at arbitrary positions of different inner layers. As a result, a change in state at an arbitrary position in the thickness direction in the inner layer and a change in state near the surface layer can be measured by replacing each with a change in resistance. next,
The through hole 11c at the right end in FIG. 2 is composed of the front side metal foil 10A formed on the surface of the substrate 3 and the front side metal foil 10A.
And means for connecting the back side metal foil 10B formed on the corresponding back side of the substrate. Since the terminal portions 10a and 10b of the front-side metal foil 10A and the back-side metal foil 10B are exposed on the surface of the substrate, it is possible to perform measurement by abutting a measurement terminal of a measuring device (not shown). Such a configuration can be easily realized by a normal printed wiring board manufacturing technique, and a change in the state of the surface layer (front surface and back surface) of the substrate can be taken out as an electric signal and used for measurement. In particular, by using a combination of the metal foils disposed on the front and back surfaces of the substrate, it is possible to measure a state change with high accuracy. If a high-precision measurement result is not desired, it is conceivable to create a metal foil gauge by a conventional wiring technique using an existing copper foil (for example, indicated by reference numeral 4) arranged in the substrate 3.

[0009]

As described above, the present invention eliminates the need for preparing a large number of strain gauges by using a printed wiring board having a built-in strain gauge made of metal foil, and also requires consideration of the space to be attached to the substrate surface. Is also gone. In addition, there is no need for a setup or procedure for pasting, which makes it very easy to handle.
If the printed wiring board is assembled to the product at the same time,
It is also possible to perform distortion measurement at any occasion as needed. In other words, according to the first aspect of the present invention, since the metal foil having a large change in the conductor resistance is disposed in the inner layer of the substrate, various changes in the state of the printed wiring board caused by external stress and the like are replaced with changes in the resistance. Can be. According to the second aspect of the present invention, the measurement electrode is arranged on the surface layer (front surface and / or back surface) of the substrate and connected to the metal foil having a large change in conductor resistance arranged in the inner layer. It can be taken out as a signal. According to the invention of claim 3, since a metal such as Ni is used as the metal foil having a large conductor resistance change, it is possible to form the metal foil in a normal printed wiring board manufacturing process, and to improve productivity. Can be increased. According to the fourth aspect of the present invention, since the metal foil gauge is formed by photoetching, the metal foil gauge can be easily formed by a normal printed wiring board manufacturing technique without using a complicated and expensive special technique.

According to the fifth aspect of the present invention, the metal foil gauges are arranged at a plurality of positions in the same inner layer, and the change in the state at each position of the lint substrate can be measured by replacing the change in the state with the change in resistance. According to the invention of claim 6, the foil gauges are arranged in multiple directions in the same inner layer, and the measurement can be performed by replacing a directional state change with a resistance change. According to the invention of claim 7, the metal foil gauge is arranged on each of the plurality of insulating plates constituting the substrate, and it is possible to measure the state change in the surface layer and the inner layer. According to the invention of claim 8, since the metal foil and the measurement electrode provided on the surface layer are connected by the through holes, it is possible to easily form the path of the electric signal by a normal printed wiring board manufacturing technique. it can. According to the ninth aspect of the present invention, since the through hole is formed by plating solder in the hole formed in the substrate, the through hole can be easily formed by a normal printed wiring board manufacturing technique, and the state changes as an electric signal. Can be taken out. According to the tenth aspect of the present invention, the metal foil gauges are relatively arranged at the uppermost portion (front surface) and the lowermost portion (back surface) of the substrate, and a highly accurate state change can be measured by a combination thereof. .

[Brief description of the drawings]

FIG. 1 is an external perspective view of an example of a printed wiring board to which the present invention has been applied.

FIG. 2 shows a metal foil (metal foil gauge) as an example of the present invention.
The figure which shows the example of a structure of FIG.

FIG. 3 is a cross-sectional view of the printed wiring board of the present invention.

[Explanation of symbols]

1 printed wiring board, 2 insulating plate, 3 substrate, 4 inner layer conductor pattern, 10 metal foil (metal foil gauge), 10
a, 10b Terminal part, 11a, 11b, 11c Through hole, 15 Measurement electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E317 AA24 BB02 BB12 BB15 BB18 CC31 CD29 GG20 5E338 AA03 BB63 BB75 EE60 5E346 AA02 AA12 AA14 CC01 CC25 CC32 CC34 CC37 CC40 DD12 DD22 DD32 DD33 FF01 FF22 GG34 HH40

Claims (10)

[Claims] 1. A printed wiring board comprising a substrate on which a plurality of insulating plates are laminated and a conductor pattern formed on at least a surface layer of the substrate, wherein a metal foil having a large change in conductor resistance is embedded in an inner layer of the substrate. A printed wiring board characterized by the above. 2. The printed wiring board according to claim 1, wherein a measurement electrode for connecting to the metal foil is arranged on a surface layer of the substrate. 3. The method according to claim 1, wherein nickel is used as the metal foil having a large change in conductor resistance.
The printed wiring board as described. 4. The printed wiring board according to claim 1, wherein the metal foil is formed on the insulating plate by photoetching. 5. The printed wiring board according to claim 1, wherein a plurality of the metal foils are arranged at arbitrary positions on one insulating plate constituting the substrate. 6. The method according to claim 1, wherein a plurality of the metal foils are arranged on one insulating plate, and directions of the metal foils are set in multiple directions. Printed wiring board. 7. The printed wiring according to claim 1, wherein the metal foil is arranged at an arbitrary position on a different insulating plate constituting the substrate. Board. 8. The print according to claim 1, wherein the metal foil and a measurement electrode formed on a surface layer of the substrate are connected by through holes. Wiring board. 9. The print according to claim 1, wherein the through holes are formed by plating solder in the holes formed in the substrate. Wiring board. 10. A printed wiring board comprising a substrate on which a plurality of insulating plates are laminated, and a conductor pattern formed on at least the surface layer of the substrate. A printed wiring board, wherein each of the metal foils is disposed on the back surface of the substrate corresponding to the side metal foil, and both metal foils are connected by through holes.